The proposed study will broaden our understanding of how brain neurochemistry affects emotional communication in humans. Specifically, it will determine if arginine-vasopressin (AVP), an endogenous neuropeptide known to influence various social behaviors in non-human vertebrates, affects autonomic and / or somatic responses to emotional facial expressions in humans. This goal will be accomplished by measuring the effects of intranasally administered AVP in post-pubertal men and women on heart rate and skin conductance and on the electromyographic (EMG) responses of multiple facial muscles in response to facial expressions that vary in their emotional content. Preliminary results indicate that AVP selectively increases the EMG responses of the corrugator supercilii that are evoked by emotionally neutral facial expressions to levels typically seen in response to angry facial expressions in control subjects. Because corrugator supercilii activity is associated with the perception of angry / threatening social stimuli and with the generation of facial expressions related to anger towards another individual, this result suggests that AVP may affect agonistic communication processes in humans by biasing individuals to respond to emotionally ambiguous social stimuli as if they were threatening. The present study will extend that finding by determining the time course for this effect, determining if AVP affects multiple facial muscles whose coordinated activity comprises a somatic "signature" associated with the perception of threatening social stimuli, determining if ratings of the perceived sociability of emotional facial stimuli are influenced by AVP administration, and determining if AVP influences on the processing of facial stimuli are present in women as in men. The findings from this research will help elucidate the mechanisms through which this neuropeptide influences social communication in humans, particularly agonistic communication. Such knowledge may ultimately help us better understand and treat mental disorders like depression and autism, which involve, among other things, difficulties processing emotional information related to social communication.